1. Field of the Invention
This invention relates to attitude measuring systems. More particularly, the present invention system is adapted to supply the same correction information to a satellite attitude measuring system as is presently supplied by a star tracking system and/or a horizon and sun measuring system.
2. Description of the Prior Art
Attitude measuring systems for determining roll, pitch and yaw (RPY or .theta. RPY) are known and used in satellites and on aircraft to determine RPY of moving platforms. Heretofore, such moving platforms have included on board a gyro attitude package which comprises three gyros, one each for roll, pitch and yaw.
Before an aircraft takes off its gyro attitude system is calibrated and is not corrected during flight. Gyros are subject to drift and must be updated or recalibrated, accordingly, there is provided in every satellite system some type of gyro correction system. The most common calibration systems are star tracking systems that produce RPY information based on the position of known stars and horizon and sun systems which employ sun direction and horizon position information. Both of these correction systems are presently used system which employed telescopes mounted on movable gimble platforms which are accompanied with the proper control and positioning structure.
When extremely accurate attitude position is required, there is no substitute for the accuracy of a star tracking system. However, ninety percent of all the satellites that are launched do not require the accuracy of a star tracking system which is known to cost up to $1 million for each package. It would be extremely desirable to provide an attitude measuring system which is more accurate than the known horizon and sun attitude measuring system yet costs less.